Ellagic acid is a compound which is contained in plants such as strawberry, apple, guava, and tara and which has a polyphenol structure. Ellagic acid is known to have physiological functions such as a whitening effect and an antioxidant effect.
However, ellagic acid has low solubility in water and is hardly used in an aqueous product. Accordingly, a technology for solubilizing ellagic acid in water has been investigated, and for example, an α-glycoside obtained by bonding one or more molecules of a sugar to ellagic acid (Patent Document 1) has been reported. There has also been reported a method involving forming fine particles of ellagic acid by a mixing with a crystal growth inhibitor and a water-soluble polymer to disperse the particles stably (Patent Document 2).
Meanwhile, based on recent health trends, an α-amylase inhibitory action of a guava leaf extract solution has attracted attention, and for example, soft drinks each containing a guava leaf extract solution or the like have been developed (for example, Patent Documents 3 and 4).
The guava leaf extract solution contains ellagic acid, and forms precipitates at room temperature due to its poor solubility in water. Accordingly, in order to suppress deterioration of appearance of a drink, there have been proposed, for example, a method involving removing fine crystal nuclei of free ellagic acid from a guava leaf extract solution by microfiltration (Patent Document 3) and a method involving extracting guava leaves with hot water at from 90 to 98° C., concentrating the extract thus obtained to a Brix sugar content of from 20 to 30, and subjecting the resultant concentrate to freeze drying (Patent Document 4).